The present invention relates to a wireless communication device capable of transmitting and receiving data in packets after a short-range wireless communication unit is used to establish a link, and to a method of packet transmission between the wireless communication devices.
In recent years, systems adapting the Bluetooth™ standard have been developed, the Bluetooth standard uses frequency hopping in a waveband of 2.4 GHz to transmit and receive data among discrete devices. For example, devices such as cellular phones, PHSs (Personal Handyphone Systems), personal computers, and personal digital assistants are mounted with a wireless module of the Bluetooth standard and the Wireless module is used to transmit and receive data, whereby data can be transmitted and received among discrete devices. Hereafter, a device mounted with the wireless module of the Bluetooth standard is denoted as BT device.
When the BT devices have been connected through a radio rink, data can be transmitted and received among these BT devices. At this time, any one of the BT devices is operated as a master, and the other BT devices are operated as slaves.
In Bluetooth, a channel is divided into time slots having a length of 625 microsecond, and they are given slot numbers according to the Bluetooth clock of a piconet master. A slot number is given in order of 0 to 227−1, and it is returned to zero when reaching 227−1. The BT devices, both the master and slaves, transmit packets using these time slots.
In Bluetooth, the TDD (Time Division Duplex) scheme is used in which the master and the slaves alternately transmit. The master can start to transmit packets only at even numbered time slots. Then, as long as the master transmits packets to the slave itself, the slave can start to transmit packet only at odd numbered time slots placed next to the time slots where the packets have been transmitted. In addition, both the master and slaves can transmit packets extended over five time slots at maximum.
In the meantime, link types of Bluetooth have an SCO (Synchronous Connection) Oriented) link and an ACL (Asynchronous Connection-Less) link. The SCO link is circuit-switched connection in which time slots are reserved at every fixed time interval to communicate, suitable for handling voice traffic, whereas the ACL link is packet-switched connection in which time slots not reserved by the SCO link are used to communicate, suitable for handling data traffic.
FIG. 16 depicts one example of the packet (ACL packet) communication between a master and a slave 1 or slave 2 using the ACL link. In the example shown in FIG. 16, the master transmits an ACL packet having a length of five time slots to the slave 1 at an even numbered time slot 2n. At this time, the slave 1 received the ACL packet from the master is given the right to transmit an ACL packet to the master at an odd numbered time slot 2n+5. In the example shown in FIG. 16, it transmits a packet having a length of three time slots at the time slot 2n+5. In addition, even when the slave 1 does not have information to be transmitted to the master, the other slaves cannot transmit ACL packets using the time slot 2n +5 the example shown in FIG. 16, the master successively transmits an ACL packet having a length of three time slots to a slave 2 at an even numbered time slot 2n+8. The slave 2 received this transmits an ACL packet having a length of three time slots to the master at an odd numbered time slot 2n+11.